1. Field of the Invention
The present invention pertains to gate valves or slot valves of the type used in vacuum contained automated substrate handling systems, such as may commonly be employed in modular robotic wafer fabricating systems.
2. Related Art
In the semiconductor industry, automated silicon wafer substrate handling systems are utilized to move wafers into and out of process modules that perform various operations on the wafers, such as vapor deposition, ionization, etching, etc. These handling systems are commonly referred to as cluster tools, and an example of such a system is the Marathon Series cluster platforms available from Brooks Automation, Lowell, Mass., USA.
The processes performed on the wafers are done within vacuum chambers, and the cluster platforms and associated equipment are housed in xe2x80x9ccleanxe2x80x9d rooms, the environments of which are strictly controlled. Vacuum chambers and clean rooms are utilized in order to prevent the smallest of particles from being introduced into the wafer matrices In addition, the wafer processing equipment of cluster tools is designed for low particulate generation through millions of cycles of operation. To achieve ultrapure fabrication techniques, processing equipment is employed that has a minimum of moving parts, and to further prevent particle contamination, machine componentry is properly isolated and sealed.
With clean rooms, space utilization is of utmost importance, as the costs for operating a clean room are extremely expensive. Accordingly, there is an advantage in providing more efficient equipment in less space, in order to lower manufacturing costs.
Gate valves (or slot valves) are commonly employed to provide vacuum seals at numerous locations between modular integrated processing equipment. For example, gate valves are positioned between wafer cassette modules and central handling modules, and between central handling modules and process modules. Gate valves open to allow transfer of wafers between modules, and close to seal off modules so that vacuum controlled processes may be performed within the modules.
Present gate valve assemblies include generally a gate valve housing and an actuator housing with associated controls. While these gate valve designs provide narrow profiles, allowing closely adjacent positioning of cooperating modules, the height of such gate valve assemblies can be extensive, which causes space utilization concerns below the processing equipment where associated controls and pumps are positioned. Accordingly, advantages can be achieved in space utilization by reducing the size of all processing and handling equipment, particularly gate valves. The action from components of the present valve are confined within a housing having a height considerably less than conventional actuating systems. This is accomplished, in part, by confining actuating elements within the housing.
Briefly described, the present invention comprises a slot valve for creating an air tight seal to a vacuum chamber, wherein the slot valve includes a valve housing defining a valve chamber. The valve housing has first and second aligned openings from one side of the valve housing to the other side. A valve holder is provided that is longitudinally reciprocable within the valve housing between a first holder position remote from the openings and a second holder position between the openings. The slot valve also includes a valve gate with a seal that is transversely reciprocable within the holder between a first gate position spaced from the openings and a second gate position sealing off one opening. A first actuator is provided within the valve chamber for moving the valve holder between first and second holder positions. A second actuator is carried on the valve holder for moving the valve gate between first and second gate positions. The first and second actuators are positioned within the valve housing, which creates a low profile housing for the slot valve.
According to an aspect of the invention, the second actuator is pneumatically powered to seat the valve gate into engagement about the first opening and is mechanically biased to unseat the valve gate out of engagement about the first opening.
According to another aspect of the invention, the second actuator comprises an expandable bellows chamber mounted at one end to the valve holder and mounted at its other end to the valve gate. The first actuator is pneumatically powered to move the valve holder between first and second holder positions. Pneumatic controls are provided for controlling operation of the first and second actuators. The pneumatic controls are adapted to deliver high pressure to the second actuator to seat the valve gate, with the high pressure being sufficient to overcome the mechanical biasing force attempting to unseat the valve gate.
Preferably, the pneumatic controls are adapted to apply a low pressure to the first actuator to move the valve holder between first and second holder positions. The first pneumatic actuator includes a first working chamber for receiving low pressure air to move the valve holder to the second holder position. The first working chamber of the first actuator and the second actuator are in fluid communication with each other. By controlling the first and second actuators via a common fluid source, the number of moving components necessary to seat the valve gate is substantially reduced.
The pneumatic controls are adapted to introduce high pressure air through the first working chamber of the first actuator and into the second actuator, to seat the valve gate and seal the opening. The first actuator includes a second working chamber for receiving low pressure air to move the valve holder from the second to the first holder position. Wherein upon introduction of low pressure air into the second working chamber of the first actuator, the first actuator does not move the valve holder back to the first holder position until high pressure in the first working chamber drops below the low pressure in the second working chamber, allowing time for the mechanical biasing force to unseat the valve gate.
Preferably, the mechanical biasing force unseats the valve gate at a pressure between the high and low pressures.
The present invention also includes a control system for moving a valve gate longitudinally between first and second holder positions into and out of a flow path and transversely between first and second gate positions into and out of seating engagement with a valve seat, for sealing off the flow path. The control system includes a first pneumatic actuator for moving the valve gate between the first and second holder positions into and out of the flow path. The first pneumatic actuator includes a first working chamber for moving the valve gate from the first to the second holder position into the flow path and a second working chamber for moving the valve gate from the second to the first holder position out of the flow path. The control system also includes a second pneumatic actuator for moving the valve gate into seating engagement with the valve seat. Biasing means is provided for biasing the valve gate to unseat from the valve seat. The second pneumatic actuator and the first working chamber of the first pneumatic actuator are in fluid communication with each other. The control system also includes a high pressure source for providing high pressure air to the first working chamber of the first actuator and to the second actuator, and a low pressure source for providing low pressure air to the first and second working chambers of the first actuator. The pressure necessary to overcome the biasing force of the biasing means to seat the valve gate is between the high and low pressures. In operation, low pressure introduced into the first working chamber moves the valve gate into the second position and high pressure introduced into the first working chamber and into the second actuator overcomes the biasing force of the biasing means and seats the valve gate and seals the flow path. Introduction of low pressure into the second working chamber and venting of high pressure from the second actuator and to the first working chamber first causes the biasing force to overcome the pressure in the second actuator and thereby causing the valve gate to unseat, and then causes the pressure in the first chamber to drop below the low pressure in the second working chamber, causing the valve gate to move out of the flow path.
These and other features, objects, and advantages of the present invention will become apparent from the following description of the best mode, when read in conjunction with the accompanying drawings, and the claims, which are all incorporated herein as part of the disclosure of the invention.